Microblogs such as Sina’s Weibo allow users to issue messages of a maximum of 140 Chinese characters that can course through tens of millions users everyday, defying censors with posts on sensitive topics such as human rights and the foibles of the top leadership.

The new rule was quickly mocked by microbloggers whose posts in many cases have sparked off national online protests against official corruption and reported events such as the deadly collision of a bullet train this year quicker and more accurately than official media.

“I say a couple of things, and they’re going to come get me?” said one, using the name Pan Gui. “China has more than a billion people; if a few hundred million complain are they going to have a place to put them all away?”

“What’s this about?” wrote another, posting as Wang Weijin. “They want to control our freedom of speech???”

It is not clear how many microbloggers there are among China’s nearly half-billion Internet users. Some estimates say 300 million.

But Xinhua quoted Tong Liqiang, executive deputy director of the Beijing Internet Information Office, as putting the number at 63 million — with 600 million microblog IDs in Beijing alone. But many are unused dummy accounts.

Websites in Guangzhou and Shenzhen cities in Guangdong including Tencent Holdings Ltd, China’s biggest Internet company by revenue, will only require newly registering users to provide their real names, the report said.

Users will continue to be allowed to post using their real names or pseudonyms.

The new regulation is intended to “foster healthy Internet culture” and “strengthen management and guide social networking services and instant-messaging tools,” Xinhua quoted a statement from Guangdong province as saying.

“Experts claim the new rules will purify the Internet environment, as fake and fraudulent information is often seen spreading through microblogs, which are gaining popularity among users.”

Last week Beijing authorities gave all Weibo users 90 days to register their real names or face unspecified consequences.